Perhaps you have been put on an impromptu space flight. Perhaps you're trapped with minimal supplies . . . in the Atacama Desert. Perhaps you're just bored and want to figure out how strong a stomach you have. Whatever your reasoning, learn about the right way to filter urine.

Well, you've got yourself in a pickle now, haven't you? No water, lots of heat, and only one form of liquid to drink. Let's start out by saying that you technically don't have to even filter your urine at all to drink it. Once the body is done with liquid it has seen the stomach acids, the immune system, and the kidneys, and there isn't too much bad stuff left in it. Provided you were healthy when you wandered into the desert or crash landed on Mars with only an oxygen tank and helmet, or were trapped in that meat locker when the zombies attacked, your urine is sterile. In order to keep it that way, it's best not to agonize about it. That gives it time and space to get contaminated by the world around you. Just sip it down.

Don't try drinking urine for very long, though. What is left in it can mess you up. Urine is about ninety-five percent water. The kidneys, though, have deposited extra sodium, potassium, and other minerals there. They were extra for a reason. If they get back into the body, they can do damage and dehydrate people even further. There's also uric acid in urine, and over time that will cause your mouth and gums to get very sore and damaged. Although people have used urine to stay alive in an emergency — most famously the man who had to cut off his own arm when it got trapped under a boulder while he was rock climbing — it's s stop-gap solution at best.

What you need is filtration. And there are a couple of ways to get it. If you have access to fire and plastics, it's the same as filtering sea water. Boil the urine and collect the steam on glass or plastic. The best way is to have two bottles and a long stretch of plastic tubing between them. Putting urine in one bottle and boiling it will push the steam along the tube until it condenses into drinkable water.

NASA has another solution, and its simple osmosis. Two fluids are in a bag. One is sugar solution, highly concentrated, and the other is human urine. Technically, the online NASA demonstration stated that it was 'dirty water,' but we all know what that means. The membrane between the two bags allows the water molecules, and only the water molecules, to get drawn through, lured by the high concentration of sugar molecules one one side and the relatively low concentration of salt on the other. The resulting liquid tastes a little like a sports drink, according to officials, and is more drinkable than a lot of water from the tap. What an appetizing thought.

Lastly, and this is a big one apparently, is whether a plain water filter would work. While plenty of water filters, including one that is the name of a character in Community, remove a lot of harmful stuff from water, they won't remove everything. Most filters are just glorified sieves. They're very fine meshes with holes that are as small as half a micron. This will handily filter out bacteria, but urine doesn't have much of that anyway. There are filters made of what's called activated carbon, mostly because people didn't want to market it as really porous charcoal. Carbon will trap a lot of chemicals that are in clean and treated water, but some people think taste unpleasant. What commercial filters won't generally do is filter out sodium molecules, which is why people need, really, to treat their urine in the first place. Although a filter can't hurt, if that's what you've got, and make take out some of the molecules, it just won't be enough. Better to stick to plastic tubing, or osmosis, or, you know, the tap. You can't be that bored.